"bent piece of metal with pointed ends," late 13c., from Old English stapol "post, pillar, trunk of a tree, steps to a house," from Proto-Germanic *stapulaz "pillar" (cognates: Old Saxon stapal "candle, small tub," Old Frisian stapul "stem of a tooth," Dutch stapel "a prop, foot-rest, seat," Middle Low German stapel "block for executions," German Stapel "stake, beam"), from *stap-, from PIE stebh- (see staff (n.)).

A general Germanic word that apparently evolved a specialized meaning in English, though OED finds the connection unclear and suggests the later sense in English might not be the same word. Meaning "piece of thin wire driven through papers to hold them together" is attested from 1895.

"principal article grown or made in a country or district," early 15c., "official market for some class of merchandise," from Anglo-French estaple (14c.), Old French estaple "counter, stall; regulated market, depot," from a Germanic source akin to Middle Low German stapol, Middle Dutch stapel "market," literally "pillar, foundation," from the same source as staple (n.1), the notion perhaps being of market stalls behind pillars of an arcade, or else of a raised platform where the king's deputies administered judgment.

The sense of "principle article grown or made in a place" is 1610s, short for staple ware "wares and goods from a market" (early 15c.). Meaning "principle element or ingredient in anything" is from 1826. Meaning "fiber of any material used for spinning" is late 15c., of uncertain origin, and perhaps an unrelated word.